Diversity and evolution of annelids with emphasis on Spionidae
Type of DegreePhD Dissertation
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Annelida is a diverse phylum with over 21,000 species described that occupy a variety of environments including marine, terrestrial, and fresh water. This group includes earthworms, leeches, and marine segmented worms. Although, there are some exceptions in which segmentation is highly modified (e.g., siboglinids), incomplete (e.g., echiurids), or uncertain (e.g., sipunculans). Sequencing data and phylogenomic analyses in the last decades provided a well-supported annelid backbone tree, but many areas of the annelid tree are still poorly resolved. The goal of this dissertation is to integrate and develop methods to study morphological and molecular diversity in annelids. This study contains four research chapters. The first two chapters explore the use of an integrative taxonomic approach that involves a combination of morphological data, COI barcoding, and whole mitochondrial genomes to assess diversity and biogeography of particular annelid groups. More specifically, I examined morphological and genetic diversity of the scale worm Polyeunoa laevis (Polynoidae), and its association with the soft coral Thouarella (Primnoidae) from the Southern Ocean and found that for both taxonomic groups biodiversity in the Southern Ocean appears to be underestimated. Following the integrative approach, I studied the diversity and phylogenetic relationships of Laonice (Spionidae) from Iceland, a group of spionid-annelids with a higher diversity in deep waters. Although this study was hampered by quality of preservation of animals, several species that were previously known to science were recovered (e.g., Laonice blakei, Laonice sarsi, Laonice cf. norgensis, and Laonice cirrata) and one new species was described (Laonice plumisetosa). Moreover, this study provides a preliminary phylogeny for Laonice. The third research chapter provides a description of the development of musculature, nervous system, and cilitiation patterns during larval formation of Pseudopolydora paucibranchiata using confocal laser scanning microscopy. In contrast to other planktotrophic annelid larvae, P. paucibranchiata shows a simultaneous development of muscles associated with the body wall and digestive system. Ciliation is extensive and includes multiple ciliary cells around the head, stomodeum and gut, and on the pygidium. Interestingly, no apical tuft is distinguished. The location of the first serotonergic cells could not be determined, as early larval stages showed no serotonergic activity. Thus, to study the development of the nervous system in spionid larvae, other markers will certainly be required. Lastly, phylogenetic relationships of Spionidae are explored using a combination of WGS data and previously collected transcriptome data. Taxon sampling includes 21 Operational Taxonomic Units (OTUs) representing 17 spionid genera, as well as 1 trochochaetid, and 2 sabellarid annelids as the outgroups. Maximum likelihood phylogenetic recovered two major groups with high support. Clade 1 includes the Polydora-complex, Pygospio, Spio, Scolecolepides, Scolelepis, Dispio, Lindaspio and Rhynchospio. Clade 2 includes the Prionospio-complex, Aonides, Spiophanes, and Laonice. Importantly, Trochochaeta was recovered as the sister taxon to all spionid taxa, directly contrasting previous phylogenetic studies which suggested Spionidae represented a paraphyletic group. In addition to supporting Spionidae as monophyletic using WGS datasets, this study provides a well-resolved backbone within the family for the evolutionary relationships of 17 spionid genera, yielding a dataset which is highly reproducible and can be readily appropriated for future studies.